A rotor with embedded permanent magnets has been proposed to reduce torque ripple in a rotor with embedded permanent magnets where the phase of a current is difficult to control (See Patent Document 1, for example). The rotor with embedded permanent magnets has permanent magnets embedded in an approximately cylindrical rotor core in a longitudinal direction. The rotor with embedded permanent magnets has a plurality of slits elongated from a vicinity of each permanent magnet on the outer circumferential side of the rotor core to a vicinity of the outer surface of the rotor.
A permanent magnet motor has also been proposed in pursuit of achieving a highly efficient permanent magnet motor with low noise and low vibration. The permanent magnet motor is designed to reduce armature reaction flux and also improve magnetic flux distribution of a core at an outer circumference (See Patent Document 2, for example). The permanent magnet motor is characterized by including permanent magnet holding slots, which are formed in a rotor core in portions corresponding to the respective sides of an approximately regular polygon whose center is at the axial center of the rotor core; permanent magnets embedded in the respective permanent magnetic holding slots; and four or more radially elongated slits, which are formed in the core on the outer circumferential side of the permanent magnet holding slots, and are spaced from each other along each of the permanent magnet holding slots. The permanent magnet motor is also characterized in that the pitches of the slits in end portions (near the outer circumference of the rotor core) in the radial direction are made approximately equal, and the pitches of the slits in inner portions in the radial direction are made varied so that a pitch in a portion near the permanent magnet center is the largest, and pitches then decrease with distance from the center to the ends.    Patent Document 1: P11-187597A    Patent Document 2: P2005-94968A